The Groove Tubes SAG-FST (Fender Soft Touch) preamp vacuum tube set is chosen with Blues and Jazz players in mind.

Specially selected from premium Groove Tubes preamp tubes which have been tested to meet the GT standard. Special Applications Group (SAG) provides further testing and grading for certain performance characteristics.

This 3-tube set is optimized for Fender amps which uss 12AX7 or 7025 tubes in V1 and V2.SAG-FST includes two lower gain preamp tubes to be used in the V1 and V2 positions, and one MPI (matched phase inverter) 12AT7 tube for the V6 position (in the case of blackface amps).

The rise time of the V1 and V2 tubes will increase the compression in the amp's front end, while at the same time reducing background noise. A larger percentage of distortion will be generated by the output section rather than the preamp section, resulting in increased clean headroom as another benefit.

The matched phase inverter tube will assure a balanced output section when used with matched power tubes (highly recommended) which will assure sustain across the entire range of your instrument.

Each of the three kit tubes is marked as to it's specific rating. In the future if you wish to change your gain structure, it is a simple matter to request a higher or lower value as the actual characteristics of your amplifier's gain stage is now known.

The MPI (Matched Phase Inverter) is a SAG Selected 12AT7 as is standard Fender practice.

I have purchased two sets of these tubes. The first set went into a 1979 Fender Twin reverb. It did wonders for sound. Highs and bass became very balanced. The second set went into a 1969 Fender Bandmaster Reverb. I thought the amp became dark prior to the installation of the new tubes. Then, the original tubes began to fail. I replaced the preamp tubes with this set. It did the same for the Bandmaster Reverb as it did the twin. These tubes give a very even sound for your amp. I would buy again.